A plasma display panel (hereinafter simply referred to as “panel”), typically an AC surface discharge panel, comprises numbers of discharge cells formed between a front plate and a back plate confronting each other.
The front plate comprises display electrode pairs each one of which is formed of a scan electrode and a sustain electrode, and the display electrode pairs are formed in parallel to each other on a front glass substrate. A dielectric layer and a protective layer are formed such that those two layers cover the display electrode pairs. The back plate comprises a plurality of data electrodes formed in parallel to each other and on a back glass substrate, a dielectric layer covering the plurality of data electrodes, and a plurality of barrier ribs formed in parallel with the data electrodes and on the dielectric layer. The dielectric layer has a phosphor layer on its surface, and the barrier ribs have phosphor layers on their lateral faces.
The front plate confronts the back plate such that the display electrode pairs and the data electrodes form two-level crossings. The front plate and the back plate are sealed, and discharge gas is filled in a discharge space of the sealed body. The discharge gas includes, e.g. xenon at 5% partial pressure ratio. In the foregoing panel, gas-discharge in respective discharge cells will generate ultraviolet rays, which then excite the phosphors and emit light in respective colors, i.e. Red, Green and Blue, thereby displaying a color display.
A sub-field method is widely used for driving the panel. According to this method, one field period is divided into a plurality of sub-fields, then a combination of the sub-fields, which are supposed to emit light, allows displaying a gradation.
Each one of sub-fields has an initializing period, an addressing period, and a sustained period. During the initializing period, an initializing discharge takes place, so that wall charges necessary for addressing performance coming next are formed on the respective electrodes. To be more specific, there are two types of initialization, one is an entire initialization, i.e. the cells involved are entirely initialized for generating an initializing discharge (hereinafter referred to an entire initialization), and the other is a selective initialization, i.e. only the discharge cells that carried out the sustain discharge are selected and initialized for generating an initializing discharge (hereinafter referred to as a selective initialization).
During the addressing period, an address discharge is generated selectively at discharge cells to be used for displaying, so that wall charges are formed. During the sustained period, a sustain pulse is applied to alternately the display electrode pair formed of a scan electrode and a sustain electrode, thereby generating sustain discharges at the discharge cells where address discharges are take place, and illuminating the phosphor layers of the corresponding discharge cells. A video can be thus displayed.
There is another sub-field method, which uses a voltage waveform gently changing for the initializing discharge to take place, and the initializing discharge also takes place selectively at discharge cells in which sustain discharges have taken place, so that light emission not involved with the grayscale display can be reduced as much as possible. This method thus can increase the contrast ratio. To be more specific, e.g. during the initializing period of a sub-field among a plurality of sub-fields, an entire initialization is carried out, i.e. the entire cells are initialized for discharging, and during the initializing periods of the other sub-fields, a selective initialization takes place for initializing the selected discharge cells in which sustain discharges have taken place. As a result, light emission not involved with the display takes place only at the light emission accompanying the entire initialization, so that a display at a greater contrast ratio is obtainable (e.g. refer to cited patent reference 1.)
The driving method discussed above needs light emission not involved with the video display, i.e. luminance in black-display area at no video (hereinafter referred to simply as “black luminance”) is formed of only faint light emission accompanying the entire initialization, so that a video at a higher contrast ration can be displayed.
Panels having a higher resolution and a larger screen are introduced in the market, and this market trend needs the more numbers of discharge cells. On top of that, the number of sub-fields needs to increase for improving a pseudo contour of a dynamic picture image as well as a picture quality. These requirements need a higher speed of addressing performance.
The entire initialization that initializes all the discharge cells not only forms wall charges necessary for the addressing performance as discussed above, but also generates a priming that decreases a discharge delay and steadily generates the address discharge. Thus increment of the priming is effective to perform the addressing operation at a higher speed. However, a simple increment of the number of the entire initializations raises the black luminance, and lowers the contrast ratio, so that the picture quality is lowered.
Another driving method for overcoming the foregoing problem is disclosed in, e.g. cited patent reference 2: Based on the average picture level (APL) of a video signal to be displayed, the initialization during the initializing period of respective sub-fields is determined to be an entire initialization or a selective initialization, so that the number of the entire initializations can be varied, which allows steady addressing at a higher speed while the rise of black luminance is suppressed.
However, the variation in the number of the entire initializations as discussed above sometimes discontinuously varies the black luminance that should be kept constant, and then the picture quality is lowered. Meanwhile the number of sub-fields in one field, in which sub-fields the entire initializations take place, is referred to as the number of entire initializations. The cited patent references 1 and 2 discussed above are actually the following ones:
Cited patent reference 1: Unexamined Japanese Patent Publication No. 2000-242224, and Cited patent reference 2: Unexamined Japanese Patent Publication No. 2005-215132.